This invention relates to a circuit for rejecting noise signals and passing valid signals, and in particular to a circuit for distinguishing between horizontal synchronizing (H sync) pulses derived from an off-tape video signal and spurious noise pulses.
In video tape signal processing systems, a periodic H sync pulse of defined frequency and phase is used to synchronize the horizontal lines of the television image to prevent distortion and instability of the picture. It is generally known that in such video tape systems, video signals recorded on tape and then played back, are subject to variations in speed and tape tension and accompanying phase shifts. Also, phase shifts of the video signal occur due to eccentricities in the mechanical tape drive elements, such as the capstan or drive motor pulleys. In addition, the recorded video signal may contain spurious noise signals which also are recovered on playback. These factors affect the phase and therefore the synchronization of the horizontal lines thus degrading the integrity of the television picture.
In order to provide a reference for indicating when a phase shift has occurred, the video signal includes as a reference a periodic horizontal sync pulse which delineates the beginning of each horizontal line of the television image. However, if there is a phase shift of the reference horizontal sync pulse, the phase shifted pulse will cause the respective horizontal line to be out of alignment, which results in the degradation and distortion of the television picture. Therefore compensation and correction for the undesirable phase shift must be provided to afford a correct representation of the television picture.